How to Tell if Object is No Longer in Camera View (bpy)
Yes there's an easy way, go to the BGE Documentation to look for more information. Since you dont specified if you are using bpy or bge i go for bge.

from bge import logic
cont = logic.getCurrentController()
cam = cont.owner

# Test point [0.0, 0.0, 0.0]
if (cam.pointInsideFrustum([0.0, 0.0, 0.0])):
  # Point is inside frustum !
  # Do something useful !
else:
  # Box is outside the frustum !